At present, people usually boil water using an electric kettle, and then pour the boiled water into a thermos bottle for insulated storage, which results in inconvenient handling. Consequently, a kind of electric thermos jug was invented that could boil water and preserve heat. It worked using two heating elements, namely, a main heating element with large power and a heating element with low power for keeping water hot by intermittent heating. This structure could maintain water temperature within the preset range for a long time, but it was not provided with heat insulation measures. Therefore, water in the jug had to be boiled frequently and repeatedly, which not only had a bad influence on water quality, but also wasted electricity.
As a result, an electric thermos jug with single heating element was invented, which body was covered with heat insulating material, or, had a double-layer with vacuum gap. It increased greatly thermal insulation and reduced heating frequency. Still, its bottom for heating had good thermal conduction. Consequently there was a swift heat loss from the bottom. Besides, the lid was designed as single-layer structure, and for safety reasons the lid was usually provided with a steam discharge vent, or steam discharged directly from the spout to prevent explosion due to excessive steam pressure in the jug when boiling water. As a result, this structure caused heat loss from the lid or spout during the insulated storage period.